Heat-treatment for copper-nickelcobalt permanent magnet alloys



Patented Mar. 9, 1948 HEAT-TREATMENT FOR COPPER-NICKEL- CQBAL'E PERMANENT MAGNET ALLOYS Jchn D. Seaver, Marbleh General Electric Com New York cad, Mass., assignor to pany, a corporation of No Drawing. Application July 24, 1942, Serial No. 452,205

Cia-ims.

This inventionrelates to permanent magnets and more particularly to a process for heat-treating copper-nickel-cobalt permanent magnet alloys. Alloys of this composition are disclosed in the patent to Dannohl 2,170,0l7, August 22, 1939. Such alloys are machinable but cannot be rolled, drawn, or swaged without great difiiculty.

It is an object or the present invention to provide a permanent magnet alloy and a process for heat-treating permanent magnet alloys containing copper, nickel and cobalt whereby the machining of such alloys is improved and they may be easily rolled, drawn, swaged, etc. A further object is to improve the magnetic properties of such alloys.

Alloy compositions employed are substantially those disclosed in the Dannohl patent, for example, alloys containing about 20-85% copper, -50% nickel and 570% cobalt. A preferred range of compositions contains 35-60% copper, about 20-25% nickel and about 240% cobalt. The total content of copper-nickel-cobalt totals substantially 100%. An alloy containing 50% copper, 21% nickel and 29% cobalt gives satisfactory results with respect to lifting strength and is relatively low in cost,

In carrying out the present invention, the alby is given a preliminary heat treatment which comprises heating it at about 1100" C. and holding at 1100 C. for sufilcient time to destroy the pronounced segregation developed during casting, and then cooling slowly to a temperature in the neighborhood of 820 C. The cast material is heated at about 1100 C. generally for about four to eight hours. The shorter heating period may be employed with castings of very thin cross section, for example less than one-quarter of an inch. As a general rule, however, the castings should be heated for at least eight hours. A

cooling rate of about 120 C. per hour gives sat- 4 isfactory results although this rate may be increased or decreased somewhat, if desired. If the cooling rate is decreased to about 60 C. per hour the available softening of the alloy is increased about three points as measured on the Rockwell B scale. On the other hand, if the cooling rate is increased to about 240 C. per hour the available softening is decreased about two and one-half points.

If desired the proper softening rate may be obtained by [other means, for example by rapid iumace cooling the alloy from 1100 C. to about 1000 C., holding at the latter temperature for about an hour and then controlled furnace cooling of the alloy as mentioned above. In this case pointed out.

the softening obtained is substantially equal to that obtained by slowly cooling the alloy from l to about 800 to 870 C. as heretofore After the alloy has been softened and homogenized by the preliminary heat treat-- ment, it may be heavily cold reduced, for example, given a reduction of about Ell-75%.

After a preliminary heat treatment the alloy may be cold reduced, machined, drawn to shape, etc., and thereafter precipitation hardened by heating to about 1100 C. for a few minutes, for

example about five minutes, oil quenching and then heating for a few hours, for example four hours, at a temperature between about 575 C. and 650 0., preferably about 625 C. The period of time at which the alloy is held at the various temperatures is not critical but good results may be obtained by heating the alloy for the periods indicated.

If desired, after the preliminary homogenizing or after the cold reducing step the alloy may be reannealed by heating it at 1100 C. for a short time, a few minutes, and slowly coolin at a rate of about C. per hour. Such reanneal is not always necessary but may be employed as manufacturing practice dictates. After the reanneal the alloy may be most easily machined or the desired part punched out and then age hardened as hereinbefore pointed out.

The preliminary softening step and also the reanneal particularly improve the machining properties of the alloy. The reanneal is particularly applicable to rolled stock to develop maximum ductility suitable for punching or drawing intricate pieces.-

Tests on the magnetic properties of the precipitation hardened Dannohl alloy quenched from a temperature of 1100 C. gave a residual of 3195, a coercive of 642, and a (Bd Hd) max. of 677,000. The same alloy composition heat treated in accordance with the present process has a residual of 3600, a coercive of 740 and a (Bd I-Id) max. of 900,000.

While the heat treated alloy is easily machinable, a further improvement in this respect may be obtained by adding a small quantity of lead to the alloy, for example about 0.25 to 8.5%. The addition of lead to the alloy greatly improves the machinability of the alloy in the as-cast, precipitation hardened or softened condition and has no adverse effect on the magnetic properties of the alloy.

What I claim as new and desire to secure by United States Letters Patent, is:

1. A method for heat treating a permanent magnet alloy consisting substantially entirely of copper, nickel and cobalt which comprises heating the alloy at a temperature of 1100 C., slowly cooling it from at least 1000 C. to about 800 to 870 C., subjecting the alloy to mechanical work, thereafter heating the alloy at about 1100 C. for a few minutes, quenching it, and then reheating it at about 575 to 650 C. for a few hours.

2. A method for heat treating a permanent magnet alloy consisting of about 20-85% copper, 10-50% nickel, 51-70% cobalt which comprises heating the alloy at a temperature of about 1100 C. for about eight hours, then slowly cooling the alloy to about 800 to 870 C., subjecting the alloy to mechanical work, thereafter heating the alloy at about 1100 C. for a few minutes, quenching it, and then reheating it at about 575 to 650 C. for a few hours.

3. A method for heat treating a permanent magnet alloy consisting substantially entirely of copper, nickel and cobalt, which comprises heating the alloy at a temperature of about 1100 C., slowly cooling, subjecting the alloy to mechanical work, thereafter heating the alloy at about 1100 C. for a few minutes, quenching the alloy and then reheating it at about 575 to 650 C. for a few hours.

4. A method for heat treating a permanent magnet alloy consisting of about 20-85% copper, 10-50% nickel and -70% cobalt, which comprises heating the alloy to a temperature of about 1100 C. for a few hours, slowlycooling it and cold reducing the alloy about 50-75% thereafter heating 4 the alloy at about 1100 C. for a few minutes. quenching, and then reheating it at about 575 to 650 C. for about four hours.

5. A method for heat treating a permanent magnet alloy, consisting of about 20-85% copper, 10-50% nickel, 5-70% cobalt, which comprises heating the alloy at a temperature of about 1100 C., cooling it to about 820 C. at a rate of about C. per hour, cold reducing the alloy and thereafter heating the alloy to an elevated temperature to effect a condition of solution in the alloy, quenchin and thereafter aging it at a lower temperature.

JOHN D. SEAVER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,816,509 Wise July 28, 1931 1,992,325 Schwaarwachter Feb. 26, 1935 2,170,047 Dannohl Aug. 22, 1939 2,185,958 Strang Jan. 2, 1940 2,230,804 Koebel Feb. 4, 1941 2,281,691 Hensel May 5, 1941 FOREIGN PATENTS Number Country Date 386,682 Great Britain Jan. 23, 1933 

